The present invention relates to a method and apparatus for determining whether a moving entity is moving in a predetermined direction.
From U.S. Pat. No. 5,510,795 a circuit for analyzing backscatter-modulated RF signals received from a remote transponder is known. The circuit is able to determine whether the transponder is stationary or moving towards the reader or away from it and in the case that the transponder is moving, it is able to determine the rate at which the transponder is coming or going. In response to the signal received from the transponder, the circuit generates three signals, each having a different phase. By analyzing the pattern and frequency of signal state changes in the three signals, the circuit can determine the transponder's speed and direction of movement.
The Article “Relative Direction Determination in Mobile Computing Networks” by A. Kalis and T. Antonakopoulos, published in the proceedings of the IEEE Instrumentation and Measurement Technology Conference, held in Budapest, Hungary, in May 2001, describes a relative direction determination method for stations of mobile computing networks. The method uses a switched beam array for determining the direction of arrival of an incident electromagnetic field. Certain MAC layer functions are associated with different radiation patterns of the switched antenna array in order to determine the orientation of directional beams on both sides of a communication link.